Locusts are notorious as being indiscriminate devourers of everything and somewhat mindless in their attack. Although desert locusts are infamous for their swarming behavior, they usually occur in a solitary form, living alone and actively avoiding fellow locusts. The difference between a swarming locust brain and a solitary locust brain is quite extraordinary. Despite being smaller than solitary locusts, swarming locusts developed brains that were 30% larger. Not only that, regions of the brain that are dedicated to different tasks had very different proportions in the two phases.

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Locust is the name commonly given the swarming phase of short horned grasshoppers of the family Acrididae. These are species that can breed rapidly under suitable conditions and subsequently become gregarious and migratory. They form bands as nymphs and swarms as adults both of which can travel great distances, rapidly stripping fields and greatly damaging crops. When environmental conditions produce many green plants and promote breeding, locusts can congregate into thick, mobile, ravenous swarms.

A desert locust swarm can be 460 square miles in size and pack between 40 and 80 million locusts into less than half a square mile.

Like the individual animals within them, locust swarms are typically in motion and can cover vast distances. In 1954, a swarm flew from northwest Africa to Great Britain. In 1988, another made the lengthy trek from West Africa to the Caribbean.

Working with colonies of swarming locusts, Dr Swidbert Ott and Dr Stephen Rogers of the University of Cambridge, converted some of them into the solitary phase by keeping them in isolation for three generations.

Despite being smaller than solitary locusts, swarming locusts developed brains that were 30% larger. Not only that, regions of the brain that are dedicated to different tasks had very different proportions in the two phases.

In the solitary locust the parts of the brain that deal with vision and smell are proportionately larger, possibly helping them to detect faint or distant stimuli, whereas in the swarming locust huge increases in size occur in the parts of the brain associated with learning and processing complex information.

Swarming locusts need these larger brains to cope with the challenges of a life on the move that can take them across continents in a mass of other locusts, and to deal with the intense competition that dominates their existence, Dr Ott believes.

"Their bigger and profoundly different brains may help swarming locusts to survive in the cut throat environment of a locust swarm. Who gets to the food first wins and if they don't watch out, they themselves become food for other locusts. In a nutshell, you need to be brainier if you want to make it in the mayhem that is a locust swarm."

Swarming locusts seem to have bigger brains than the ordinary locust due to social pressures and the need to compete for food. But what causes the actual phase change?

In 2009 new research by a team of scientists in Cambridge and Oxford, UK and Sydney, Australia solved the question as to why locusts changed from solitary to swarming phases. They identified increase in the chemical serotonin in specific parts of the locust's nervous system as launching the fundamental changes in behavior that lead to the gregarious phase. Serotonin was formed in response to locust crowding

The new locust swelled brain results are published in the Proceedings of the Royal Society B.